Power system

ABSTRACT

The present invention provides methods and apparatus for reducing power consumption. One method includes detecting the presence of an object, identifying whether the object is a valid device and restricting power if it is not a valid device. Another method includes temporarily applying a low amount of power to the primary unit to detect a load, supplying more power to determine if it is a valid secondary device, and restricting power if it is not. An apparatus for reducing power consumption includes two power inputs, where the lower power input powers a sense circuit. A switch selectively decouples the higher power input from the primary subcircuit during detection mode and couples the higher power input to the primary subcircuit during power supply mode.

BACKGROUND OF THE INVENTION

It is more convenient to be able to power portable devices without theneed to plug in a traditional power cable into the device. For examplesome wireless power systems include a portable device that when placednear a wireless power supply unit can receive power without the need fora direct electrical contact. However, when there is no device on theunit (or when the only devices on the unit are fully charged) it ispossible to keep the power consumption at a minimum.

Some wireless power units have a standby mode, whereby it periodicallytransmits power for a short period to look for devices. If the unitdetects a valid device that is requesting power and determines thatthere are no foreign objects that would get hot or hinder power transferin the vicinity then the unit may come out of standby. The power levelof the pulses in standby mode are sufficiently high to transfer enoughpower to the portable device so that it can communicate back, because itis possible that the device's batteries may be fully depleted. Thelength of the pulses are long enough to determine that the device is avalid device and that there are no foreign objects present that may gethot or otherwise interfere with the system. The time between the pulsesis short enough that the user gets quick feedback that the unit isoperational. There is therefore a limit to how low the power consumptioncan be during standby.

In addition to the power for determining the presence of devices to bepowered, there are practical limitations that increase the powerconsumption. For instance, in some inductive power supplies a DC powersource is used even between the transmitted pulses. This means thatmains rectification losses are always present and can be considerable.In some scenarios, multiple DC voltages are used and it would not bepractical to start these up within the pulse duration, so DC conversionlosses might always be present. The microprocessor in the unit thatdrives the pulse width modulation for the inverter typically isrelatively high performance and consumes a certain amount of powercontinuously.

These and other factors make it challenging for a wireless power systemto have low standby power. One attempted solution is to have a switch,so that the user switches the unit on before placing a device on it.However, this considerably detracts from the main benefit the systemprovides—the convenience of just putting the device on the wirelesspower supply. With careful design it is possible to achieve standbypowers as low as 0.5 W. However, there is a desire for these figures tobe reduced further. A typical mobile phone charger may only be used for3 hours a week and spend the rest of the time in standby. Assuming anaverage of 4 W consumption during charging and 0.5 W during standby, theannual energy consumption would be 0.624 kWH to charge the phone and4.38 kWH whilst in standby. This means that seven times as much energyis wasted in standby compared to the energy used. The impact of shipping100 M units (10% of annual cell phone sales in 2007) would meanapproximately 50 MW of power generation capacity just to service thestandby. There is increasing awareness that energy wastage throughelectronic devices left on standby may contribute to climate change. Asa result there are initiatives to reduce the power consumption ofelectronic devices whilst in standby.

There have been several devices aimed at reducing the standby power oftelevisions and other appliances using remote controls (U.S. Pat. No.6,330,175, WO2006106310). However, these are not applicable to wirelesspower systems.

In addition to wireless power systems, other systems for examplecontactless card systems also suffer from power wastage in standby.

SUMMARY OF THE INVENTION

The present invention is directed to methods and apparatuses forreducing power consumption in a wireless power supply.

One embodiment of a method for reducing power consumption includesdetecting the presence of an object within proximity of a primary unit,sending a pulse of power to the object in response to detectingpresence, determining whether a valid secondary device is present inproximity to the primary unit in response to sending the pulse of powerto the object, and in response to a determination that a valid secondarydevice is not present, restricting power supplied to the primary unit.

Another embodiment of a method for reducing power consumption includesapplying a pulse of low power to the primary unit, detecting whetherthere is a draw of power in the primary unit indicative of a load withinproximity of the primary unit, upon detecting a load, supplying power tothe primary unit at a higher level than the pulse of low power,determining whether a valid secondary device is present in proximity tothe primary unit in response to the supply of power at the higher level,and in response to a determination that a valid secondary device is notpresent, restricting power supplied to the primary circuit.

One embodiment of a primary unit includes a first power input, a secondpower input, a primary subcircuit capable of transferring power to asecondary device, a switch, and a sense circuit. The first power inputsupplies power during power supply mode and the second power inputsupplies power during detection mode. The second power input providesless power than the first power input. The switch selectively couplesand decouples the first power input to the primary subcircuit. The sensecircuit is powered by the second, lower, power input and detects thepresence of an object within proximity of the primary unit. Duringdetection mode the operates the switch to decouple the primarysubcircuit from the first power input. Accordingly, the primary unitconsumes less power during detection mode than during power supply mode.

Another embodiment of a primary unit includes a power supply circuit, adetection circuit, a switch to selectively couple and decouple the powersupply circuit to a supply of power, and a control circuit. The powersupply circuit wirelessly transfers power to a secondary device during apower supply mode. The detection circuit detects the presence of anobject within proximity of the primary unit during a detection mode. Thecontrol circuit alternately operates the primary unit in detection modeand power supply mode. During detection mode, the control circuitoperates the switch to decouple the power supply circuit from the supplyof power. The primary unit consumes less power during detection modethan power supply mode.

One embodiment for reducing power consumption includes providing aprimary unit capable of selectively operating in a detection mode, anidentification mode, and a power supply mode. The method also includesdetecting presence of an object within proximity of the primary unitduring the detection mode, identifying the object during identificationmode, and supplying power wirelessly to the secondary device during thepower supply mode. The detection mode includes restricting the supply ofpower to at least a portion of the primary unit, detecting the presenceof an object within proximity of the primary unit, and either staying inthe detection mode or entering the identification mode in dependenceupon the detecting. The identification mode includes identifying whetherthe detected object is a valid secondary device, upon identifying avalid secondary device entering the power supply mode, and upon failingto identify a valid secondary device entering the detection mode. Thepower supply mode includes supplying power to the primary unit at ahigher level than during the detection mode, the higher level of powersufficient for the primary unit to function as a wireless power supply.

According to a first aspect of the invention there is provided a methodfor reducing the power drawn by a primary unit capable of interactingwith a secondary device, separable from the primary unit, the methodhaving the following modes:

the first mode comprising the steps of:preventing or restricting the supply of power to the primary unit;detecting changes in the number, type, position or distance of objectsor object, in proximity to the primary unit;upon detecting said changes, entering a second mode;the second mode comprising the steps of:supplying power to the primary unit at a higher level than the firstmode;identifying if there is a secondary device in proximity;remaining in the second mode or entering the first mode in dependenceupon the identification.

The first mode may use power from a different source than the secondmode. For example, the first mode may take power from an energy storageelement. The second mode may enter the first mode if there is nosecondary device present. The second mode may also include the step ofdetermining if the primary unit should interact with the secondarydevice and if not enter the first mode. The second mode may alsodetermine if there are objects in addition to the secondary device andin consequence enter the first mode. The detection method may bedifferent from the identification method. The detection method and/oridentification method may determine an inductance or a change ininductance of the primary coil. For example, the detection method and/oridentification method may determine the inductance or inductance changeby measuring the frequency of an oscillator coupled to the primary coil.

According to a second aspect of the invention there is provided a methodfor reducing the power drawn by a primary unit used to transfer powerand/or information wirelessly to/from a secondary device, the secondarydevice being separable from the primary unit, the

method having the following modes:the first mode comprising the steps of:preventing or restricting the supply of power to the primary unit;detecting changes in the number or position of objects or object, inproximity to the primary unit;upon detecting said changes, entering a second mode;the second mode comprising the steps of:supplying power to the primary unit at a higher level than the firstmode;identifying if there is a secondary device in proximity;upon identifying that there is a secondary device entering a third mode;the third mode comprising the steps of:supplying power to the primary unit at a higher level than the firstmode;transferring power and/or information between the primary unit and thesecondary device.

The first mode may take power from a different source to the second modeand/or third mode. For example, the first and/or second mode may takepower from an energy storage element. The third mode may supply power tothe primary unit at a higher level than the second mode. The second modemay enter the first mode if there is no secondary device present and thethird mode if there is a secondary device present. The second mode mayalso include the step of determining if the primary unit should interactwith the secondary device before entering the third mode. The secondmode may also determine if there are objects in addition to thesecondary device and in consequence enter the first mode. The third modemay also determine that the primary unit and secondary device havefinished transferring power and/or information and enter the first orsecond mode.

According to a third aspect of the invention there is provided a methodfor reducing the power drawn by a primary unit capable of interactingwith a secondary device, separable from the primary unit, the methodhaving the following modes:

the first mode comprising the steps of:preventing or restricting the supply of power from the power supply tothe primary unit;taking power from an energy storage element, separate from said powersupply;identifying if there is a secondary device in proximity;upon determining that there is a secondary device entering a secondmode;the second mode comprising the steps of:supplying power to the primary unit from the power supply;

The first mode may detect that an object is in proximity beforeidentifying whether or not it is a secondary device. For example, thesecond mode may additionally supply power to the energy storage elementto recharge it.

There may also be a third mode which is entered from the second mode ifthe energy storage unit goes below a predetermined threshold, the modecomprising the steps of: supplying power to the energy storage elementto recharge it; detecting or identifying if there is a secondary devicein proximity; upon determining that there is a secondary device enteringsaid second mode; entering said first mode if the energy storage unitbecomes fully charged.

According to a fourth aspect of the invention there is provided a methodfor reducing the power drawn by a primary unit used to transfer powerand/or information wirelessly to/from a secondary device, the secondarydevice being separable from the primary unit, the method comprising thefollowing modes:

the first mode comprising the steps of: preventing or restricting thesupply of power from the power supply to the primary unit;

-   -   taking power from an energy storage element;        detecting or identifying if there is a secondary device in        proximity;        upon determining that there is a secondary device entering a        second mode;        the second mode comprising the steps of:        supplying power to the primary unit at a higher level than the        first mode;        transferring power and/or information between the primary unit        and the secondary device.

The first mode may detect that an object is in proximity beforeidentifying whether or not it is a secondary device. For example, thesecond mode may additionally supply power to the energy storage elementto recharge it.

There may also be a third mode which is entered from the second mode ifthe energy storage unit goes below a predetermined threshold, the modecomprising the steps of: supplying power to the energy storage elementto recharge it; detecting or identifying if there is a secondary devicein proximity; upon determining that there is a secondary device enteringsaid second mode; entering said first mode if the energy storage unitbecomes fully charged.

According to a fifth aspect of the invention there is provided a primaryunit for interacting with a secondary device, separable from the primaryunit, with reduced power, the primary unit comprising:

a detection unit for detecting the presence of an object in proximity tothe primary unit;an identification unit for identifying a secondary device detected bysaid detection unit,at least one switch operable for stopping or restricting the supply ofpower to at least part of the primary unit.wherein the at least one switch is operated in dependence of thedetection unit and/or the identification unit.

The detection unit may be the same as the identification unit orseparate from the identification unit. The identification unit mayrequire more power than the detection unit to operate. Theidentification unit may take its power from a different source to thedetection unit. The detection unit and/or identification unit may takepower from an energy storage element.

There may be first and second switches operable to supply power orincrease the supply of power top the primary unit, the first switchactivated by the detection unit and the second switch activated by theidentification unit.

According to a sixth aspect of the invention there is provided a primaryunit for transferring power and/or information wirelessly to/from asecondary device separable from the primary unit, with reduced power,the primary unit comprising:

a detection unit for detecting the presence of an object in proximity tothe primary unit;an identification unit for identifying a secondary device detected bysaid detection unit;at least one switch operable for stopping or restricting the supply ofpower to at least part of the primary unit;an antenna for transferring power and/or information between the primaryunit and the secondary device;wherein the at least one switch is operated in dependence of thedetection unit and/or the identification unit such that power is reducedwhen no secondary devices require power and/or information transfer.

The antenna may be coupled to the detection unit and/or theidentification unit. The detection unit may be the same as theidentification unit. The detection unit may be separate from theidentification unit. The identification unit may require more power thanthe detection unit to operate. The identification unit may take itspower from a different source to the detection unit. The detection unitand/or identification unit may take power from an energy storageelement. The identification unit may take its power from a differentsource to the detection unit.

There may be first and second switches operable to supply power to theprimary unit at different levels, the first switch activated by thedetection unit and the second switch activated by the identificationunit.

According to a seventh aspect of the invention there is provided aprimary unit for interacting with a secondary device, separable from theprimary unit, with reduced power, the primary unit comprising:

a power input for receiving power from an external source;

an energy storage unit;an identification unit for detecting and/or identifying a secondarydevice;a switch operable for stopping or restricting the supply of power fromthe power input to at least part of the primary unit;wherein in the absence of secondary devices in proximity to the primaryunit, said switch is operated to stop or restrict power and theidentification unit is powered from the energy storage unit;wherein upon the identification unit establishing a secondary devicerequiring interaction, the switch is operated to allow the supply ofpower from the power input.

The energy storage element may be recharged from the power input.

According to an eighth aspect of the invention there is provided aprimary unit for transferring power and/or information wirelesslyto/from a secondary device separable from the primary unit, with reducedpower, the primary unit comprising:

a power input for receiving power from an external source;

an energy storage unit;an identification unit for detecting and/or identifying a secondarydevice;a switch operable for stopping or restricting the supply of power fromthe power input to at least part of the primary unit;an antenna for transferring power and/or information between the primaryunit and the secondary device;wherein in the absence of secondary devices in proximity to the primaryunit, said switch is operated to stop or restrict power and theidentification unit is powered from the energy storage unit;wherein upon the identification unit establishing a secondary devicerequiring power and/or information, the switch is operated to allow thesupply of power from the power input to the antenna.

The energy storage element may be recharged from the power input.

According to a ninth aspect of the invention there is provided a systemfor transferring power and/or information between a primary unit and asecondary device, separable from the primary unit, the systemcomprising:

a primary unit, the primary unit comprising:a detection unit for detecting the presence of an object in proximity tothe primary unit;a transceiver for transmitting and/or receiving information or powerat least one switch operable for stopping or restricting the supply ofpower to at least part of the primary unit.

a secondary device, the secondary device comprising:

-   -   a transceiver for transmitting and/or receiving information or        power;

wherein when there are no secondary devices requiring power and/orinformation in proximity to the primary unit, the switch is operated tostop or restrict power;

wherein upon the detection unit detecting the presence of an object, theprimary unit receives information from any secondary devices that may bepresent;

wherein upon the primary unit determining that there is a secondarydevice present, power and/or information is exchanged between theprimary unit and the secondary device.

According to a tenth aspect of the invention there is provided a systemfor transferring power and/or information between a primary unit and asecondary device, separable from the primary unit, the systemcomprising:

a primary unit, the primary unit comprising:

-   -   a power input for receiving power from an external source;        an energy storage unit;        an identification unit for detecting and/or identifying a        secondary device;        a switch operable for stopping or restricting the supply of        power from the power input to at least part of the primary unit;        an antenna for transferring power and/or information between the        primary unit and the secondary device;        a secondary device, the secondary device comprising:        an antenna for transferring power and/or information between the        primary unit and the secondary device;        wherein in the absence of secondary devices in proximity to the        primary unit, said switch is operated to stop or restrict power        and the identification unit is powered from the energy storage        unit;        wherein upon the identification unit establishing a secondary        device requiring power and/or information, the switch is        operated to allow the supply of power from the power input to        the antenna.

According to an eleventh aspect of the invention there is provided apower supply for converting alternating current (AC) mains electricityto direct current (DC) and supplying an external device, with reducedpower dissipation, the power supply comprising:

a power input for receiving an AC voltage from the mains;

a rectifier for converting said AC voltage to a DC voltage.

a switch coupled to the power input and said rectifier;

a power output to supplying said DC voltage to the external device;

a signal input for operating the switch so as to prevent said AC voltagebeing delivered to said rectifier;

wherein an external device is able to receive DC power via the poweroutput; wherein an external device is able to operate the switch via thesignal input to prevent power being dissipated in the rectifier.

The power supply may additionally include a DC to DC converter toconvert the DC voltage from the rectifier to a different DC voltage atthe power supply output.

According to a twelfth aspect of the invention there is provided asystem for supplying power to a unit, the system comprising:

a power supply, the power supply comprising:

-   -   a power input for receiving an AC voltage from the mains;    -   a rectifier for converting said AC voltage to a DC voltage.    -   a switch coupled to the power input and said rectifier;    -   a power output to supplying said DC voltage to the external        device;        a signal input for operating the switch so as to prevent said AC        voltage being delivered to said rectifier

a unit, the unit comprising:

-   -   an energy storage element;    -   a signal output;

wherein said unit is able to receive DC power via the power output;

wherein said external device is able to operate the switch via thesignal output and signal input to prevent power being dissipated in therectifier.wherein said external device may be powered by said energy storageelement when said switch has been operated to prevent said AC voltagebeing delivered to said rectifier.

According to a thirteenth aspect of the invention there is provided anaccessory for reducing the power consumption of a unit, the accessorycomprising:

a switch, which in operation is coupled to the input power supply of theunit

a sensor for detecting the proximity of devices or objects in proximityto the unit

wherein the accessory operates the switch in dependence upon the sensor.

According to a fourteenth aspect of the invention there is provided amethod for reducing the power consumption of a pre-existing unit, themethod comprising:

adding a switch to the input power supply of said pre-existing unit

adding a sensor to the pre-existing unit for detecting devices orobjects in proximity to the pre-existing unit

operating the switch in dependence of the sensor.

According to a fifteen aspect of the invention there is provided aprimary unit for supplying power and/or information wirelessly to asecondary device, separable from the primary unit, the primary unitcomprising:

a proximity sensor;

a switch coupled between the electricity supply and the primary unit;

wherein the switch is operated in dependence of the proximity sensor;wherein substantially no power is transferred from the electricitysupply to the primary unit when there are no devices detected by theproximity sensor.

According to a sixteenth aspect of the invention there is provided asystem comprising any primary unit as above and a portable device thatmay receive power and/or information wirelessly from the primary unit.

All these aspects have the advantage that the overall power consumptionis reduced. This and other objects, advantages, and features of theinvention will be more fully understood and appreciated by reference tothe description of the current embodiment and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a prior art wireless power system

FIG. 2 shows an embodiment of an ultra low power wireless power supply

FIG. 3 shows example timing diagrams of power to the primary coil

FIG. 4 shows a representative sense circuit

FIG. 5 shows a sense circuit implementation of FIG. 4 using a comparator

FIG. 6 shows a sense circuit implementation of FIG. 4 using amicrocontroller

FIG. 7 shows representative ultra low power circuit interface to awireless power circuit

FIG. 8 shows an example state machine executed by a ULP processor

FIG. 9 shows example timing diagrams of the state machine in FIG. 8

FIG. 10 shows a single coil relay driven by complementary FETs

FIG. 11 shows a sense circuit implementation of FIG. 4 using amicrocontroller and a single coil relay

FIG. 12 shows a retro-fit application of the ultra low power system

FIG. 13 shows a sense circuit implementation of FIG. 4 using a secondrelay

FIG. 14 shows an example state machine of a wireless power system notdesigned for upgrading

FIG. 15 shows an implementation where an existing DC power supply isretained

FIG. 16 shows an embodiment of a representative rechargeable energystorage unit

FIG. 17 shows an implementation of FIG. 16 that prevents back feed intothe charging circuitry

FIG. 18 shows an example flow diagram of wireless power supply operation

FIG. 19 shows a flow diagram of wireless power supply operation in whichthere are two power states

FIG. 20 shows a timing diagram of FIG. 19

FIG. 21 shows an example flow diagram of operation in which the energystorage unit requires a relatively long recharge

FIG. 22 shows an alternative to FIG. 2 where the energy storage unitalso powers the main circuit

FIG. 23 shows an alternative to FIG. 2 in which a single processorperforms ULP and main circuit functions

FIG. 24 shows a representative sense circuit using an additional sensinginductor

FIG. 25 shows a flow diagram illustrating separate measurements made todetermine inductance change

FIG. 26 shows a sense circuit of FIG. 4 utilizing a microcontroller

FIG. 27 shows exemplary operation of the circuit of FIG. 26

FIG. 28 shows a representative sense circuit using a peak detector

FIG. 29 shows a representative sense circuit using a phase-detectioncircuitry

FIG. 30 shows an embodiment of a wireless power supply with sensecircuits using a capacitor in series with the primary coil

FIG. 31 shows an the embodiment of FIG. 2 with DC power input

FIG. 32 shows an embodiment of FIG. 2 with a smart power supply

FIG. 33 shows an embodiment of FIG. 2 where a separate storage elementis not used

FIG. 34 shows an embodiment of FIG. 33 where power input is DC

FIG. 35 shows an embodiment of FIG. 2 where a sense circuit is not used

FIG. 36 shows an embodiment of FIG. 2 where there are multiple primarycoils

FIG. 37 shows an embodiment of FIG. 36 that allows combinations ofactive primary coils

FIG. 38 shows an embodiment of FIG. 37 that allows remote control of aDC power supply

FIG. 39 shows an embodiment of FIG. 36 that allows remote control of aDC power supply

FIG. 40 shows an embodiment of FIG. 2 using a proximity sensor

FIG. 41 shows an embodiment of FIG. 2 having auxiliary mains output

FIG. 42 shows an embodiment of FIG. 2 having remote control of anauxiliary circuit

FIG. 43 shows an embodiment of FIG. 42 giving the sense circuit directaccess to the remote control

FIG. 44 shows an embodiment of FIG. 2 integrated into another electronicdevice

FIG. 45 shows an embodiment of FIG. 2 integrated into another electronicdevice

FIG. 46 shows an embodiment of FIG. 2 using radio frequencyidentification

DESCRIPTION OF THE CURRENT EMBODIMENTS

FIG. 1 shows an example of a wireless power system 100, which useselectromagnetic induction. There is a wireless power supply 102 whichtakes electrical power and transmits this power to a portable device104. The charger takes an AC electrical input from the mains. This isrectified using a mains rectifier 106 to produce DC power. This DC poweris down-converted to a lower voltage using a DC-DC Converter 108. Thedown-converted voltage is used to drive an Inverter 110. The Inverter110 generates an AC voltage which is applied to the tank circuit, whichincludes a capacitor 114 and a primary coil 112. The portable device 104has a secondary coil 116, and sometimes a resonant capacitor 118, whichcouples to the primary coil 112, thereby producing a voltage. Thisvoltage is rectified with rectifier 120 and is down-converted to a lowervoltage using a DC/DC converter 122 to supply the Load 124. The Load 124is representative of the power requiring parts of the portable device104, and includes for example the battery and charging circuit. There isa Control element 126 in the Wireless power supply 102. This is used toadjust the DC/DC converter 108 to regulate the coil voltage and generatethe pulse width modulated signals for the inverter 110. It may also usedfor device detection and to detect the presence of foreign objects whichcould adversely affect operation.

The following embodiment descriptions are not intended to limit thescope of the invention that is described, but rather to enable a personskilled in the art to make and use the invention. Like referencenumerals are used throughout the figures to designate similarcomponents.

FIG. 2 shows a wireless power supply 200 of one embodiment of theinvention. This embodiment includes a Mains Rectifier 218, a DC/DCConverter 216, an inverter 210, a capacitor 214, a primary coil 212, anda control unit 208. This embodiment also includes a switch, SW1 202, anEnergy Storage 204 unit and a Sense Circuit 206. When the Wireless powersupply or primary unit 200 is in standby (known here as ‘Ultra LowPower’ or ULP mode), SW1 202 is open, so that no power is drawn from themains. In the ultra low power mode, the only power drawing element isthe Sense Circuit 206. The Sense Circuit 206 takes its power from theEnergy Storage element 204. The Sense Circuit 206 detects when an objectis placed in (or removed from) the proximity of the Wireless powersupply 200, but does not determine whether or not the object is alegitimate object, such as a valid secondary device, nor whether or notit desires power. If the Sense Circuit 206 detects that an object hasbeen placed on (or in proximity to) the wireless power supply 200, thenSW1 202 is closed allowing the circuits in the wireless power supply 200to receive power. Optionally, the Energy Storage element 204 may takepower to be recharged when SW1 202 is closed. The Control element 208 inthe Wireless power supply 200 then determines i) whether there is avalid device present, ii) if there is a valid device whether it desirespower; iii) whether there is a foreign object present. If there is avalid device requiring power and no foreign objects present, then thecontrol unit 208 will activate the Inverter 210 to supply current to thetank circuit, which includes the primary coil 212 and capacitor 214, todeliver power to the portable device (not shown).

Foreign objects may be detected using a method disclosed in GB2414121,which is incorporated herein by reference. If a valid device isdetected, then it communicates its power requirement to the WirelessPower Supply 200. The wireless power supply 200 measures the power beingdrawn from the primary coil 212 and compares it to the power requirementcommunicated by the device. In one embodiment, if there is nosignificant difference between the two values then the wireless powersupply 200 determines that there is a valid device and no foreignobjects present and therefore enables full power delivery to the device.

One advantage of this arrangement is that the Sense Circuit 206 can bemade to consume very low power, because it does not need to do anythingmore complicated than determine if a change in inductance has takenplace. The inductance change threshold can be set to be relatively lowto get high sensitivity. A false trigger will not have a dramatic effecton power consumption, as the Control Unit 208 in the wireless powersupply 200 will optionally make sure that there is a valid device beforedelivering full power. In general, the current to sense an inductancechange is far lower than the current to transfer power to the portabledevice and hence a significant power saving is possible. It should benoted that these switches can be configured to isolate the sense circuit206 and minimize losses. It should also be noted that alternatives usingblocking diodes and various switch circuits may provide an alternativesolution with minimal losses.

FIG. 3 shows example timing diagrams of the power delivered to theprimary coil 212 (not to scale). FIG. 3( a) shows an example when aforeign object is placed on the wireless power supply 200 at time A.Periodically, the sense circuit 206 powers up to see if an inductancechange has occurred since the previous measurement. After the foreignobject has been placed on the wireless power supply 200, an inductancechange will be detected at the next sense point, B. This will thentrigger the system to connect the mains. At point C, the system willlook to see if it is a valid device, whether it requires power andwhether there are foreign objects present. As the object is foreign, thesystem will not power up, but will remain in ultra low power mode. Atthe next sense point D, the inductance will be the same as that at pointB because the foreign object is still there. Accordingly no inductancechange will be observed and the system will remain in ultra low powermode. It will remain in ultra low power mode until the next inductancechange. When the object is removed, this will cause another inductancechange and the system will again look for valid devices.

FIG. 3( b) shows an example timing diagram when a valid device is placedon the wireless power supply 200 at time E. At the next sense point(time F), the wireless power supply 200 will detect the inductancechange, connect the mains and at point G look for valid devices. It willdetermine that a valid device is present. As a result at point H thesystem will deliver full power to the portable device. When the deviceis fully charged, the control unit 208 will determine that no furtherpower is required and place the system in ultra low power mode(providing there are no other valid devices requiring power). Removingthe device will trigger The Sense Circuit 206, but full power will onlybe delivered when a valid device requiring power is placed on thewireless power supply 200. It should be noted that the system is able towork if both a foreign object and a valid device are placed at the sametime. It is also able to work if multiple foreign objects are placed atthe same time but removed at different times and vice versa.

FIG. 3( c) shows an example timing diagram when there is a devicereceiving power and subsequently this device no longer requires power(for example because it has become fully charged or because the devicewas removed). At point I the wireless power supply 200 is deliveringpower to the device (or devices) present. At point J the systemdetermines that there are now no devices requiring power and thereforestops delivering power. At point K, the system performs a calibrationinductance measurement. This is the inductance measurement thatsubsequent measurements will be compared to in order to trigger theSense Circuit 206. This may take longer than a normal measurement as itis important to make sure that the calibration measurement is a validone and not a rogue measurement. At point L the system makes anothercheck to determine if there are valid devices present, as it is possiblethat a device may have been placed on the unit just before theCalibration measurement was made. Assuming no devices were detected, atpoint M the system goes into the ultra low power state in which lowpower inductance measurements are periodically made to sense for anotherdevice being placed in proximity.

FIG. 4 shows one way of implementing the Sense Circuit 206. In thisembodiment, the Sense Circuit 206 uses a variable frequency oscillatorto detect the inductance change. The Sense circuit 206 has an Oscillator402, the frequency of which is determined in part by an externalinductance. This external inductance is provided by the primary coil212. If the primary coil 212 has one end connected to ground, then itcan be advantageous to use an oscillator topology in which the inductoris ground connected. This enables the primary coil 212 to be connectedto the Sense Circuit 206 using a single switch. Rather than directlyconnecting the primary coil 212 to the Sense Circuit 206, the primarycoil 212 can be inductively coupled (for example by winding turns aroundthe primary coil 212 lead) or capacitively coupled using an externalcapacitor or capacitance. In the example shown in FIG. 4, the coil 212,Lp is coupled to the Oscillator 402 via SW3 404. The output of theOscillator 402 is coupled to the digital input of a microprocessor unit(MPU) 406. The Oscillator 402 may have a digital, sinusoidal or otheroutput. However, if a non-digital output is used, this signal may beconverted to a digital one prior to the MPU 406 (for example using acomparator). Irrespective of the form of output, a sinusoidal current inthe inductor may be formed, so as to prevent unwanted harmonics frombeing a cause of electromagnetic interference. In some embodiments, theinductor coil can radiate across a wide frequency range. The MPU 406makes a relative measurement of the inductance by measuring thefrequency of the signal. This is achieved by using internal counterswithin the MPU 406 and counting the number of pulses within a definedtime interval.

FIG. 5 shows the Sense Circuit 206 using one type of oscillator 402,based on a comparator 502. This type of oscillator 402 is well known.See for examplehttp://ironbark.bendigo.latrobe.edu.au/˜rice/lc/index2.html. In thistype of oscillator 402, the active component is a comparator (Comp) 502which provides a maximum output if the non-inverting (+I/P) input isgreater than the inverting (−I/P) and a minimum output (normally either0V or close to the negative supply) otherwise. The frequency isdetermined by the resonant LC tank provided by Lp 212 and C1. C1 may bechosen such that the resonant frequency of the LC circuit, 1/(2π√(LC)),is midway between the frequency input range of the microprocessor andlow enough that there is no unwanted radiation from the coil. Forexample, if the primary coil 212 has an inductance of 60 μH then a valueof C1 of approximately 2 nF gives a resonant frequency of 460 kHz. The 2nF value can be realised using two 1 nF capacitors in parallel. Manymicroprocessors allow inputs of 1 MHz frequency, so this gives a widerange of frequency variation. The resonant frequency will typically bereduced when a valid device is placed on it if it contains ferrite ormaterial with properties similar to ferrite. For example, the device mayhave a ferrite core or the device may include materials with highersaturation properties. However metal objects will tend to increase thefrequency. In addition to allowing for the inductance change caused byobjects and devices, a wide frequency range is available to cope withcomponent tolerances of both the coil and C1. It may also be useful inmultiple coil systems as will become apparent later.

The tank circuit is AC coupled to the noninverting input via capacitorC2. The value of C2 should be large to present a low impedance for ACsignals. However large capacitors occupy more space and cost more. Inone embodiment, a good compromise is 100 nF as this allows anon-electrolytic ceramic capacitor to be used which is both cheap andsmall. DC bias is provided to the noninverting input via a potentialdivider formed between resistors R1 and R2. R1 and R2 should beapproximately equal to bias the non-inverting input midway between thesupply rails. They should be large so as to reduce the bias currentbetween the supply rails, as this will result in power consumption.However it is possible that they be small relative to the inputimpedance of the comparator 502. A compromise is to make R1=R2=100 k.This should be a factor of 10 less than the input impedance. With a 3Vsupply this will result in only 15 μA current (45 μW power dissipation)in the bias resistors. Additional positive feedback is provided byresistor R4 (typically 100 k) which can improve the transientperformance. DC negative feedback is provided by R3 and brings theinverting input to the same DC value as the non-inverting input midwaybetween the supply rails. Capacitor C3 provides an AC short circuitbetween the inverting input and ground to prevent spurious noise. C3 cantake a value of 100 nF for similar reasons to C2.

The oscillator 402 will start from spurious noise at the input to thehigh gain comparator 502. The signal across the LC tank circuit will besinusoidal. The output from the comparator however will be digital,thereby enabling direct connection to the microprocessor unit (MPU) 406digital input (OSC I/P). The supply for the MPU 406, the comparator 502and the bias resistors is provided from the Energy Storage Unit 204. TheMPU 406 is configured so that the OSC I/P is connected to its internalcounter. The MPU 406 resets the counter and waits for a specificpredetermined time period. At the end of the time period, the MPU 406reads the counter and uses this value as the indicated inductancemeasurement. The MPU 406 will initially take a measurement and store it.It will periodically take measurements until a measurement is taken thatis sufficiently different from the initial measurement indicating thatan inductance change has occurred (as opposed to noise). The SenseCircuit 206 will then respond to this inductance change by appropriatelyaltering its outputs to control external switch(s).

An advantage of this type of oscillator 402 is that it starts up quicklyowing to the high gain of the comparator 502 and also that it canoscillate over a wide frequency range and a wide power supply voltagerange. This later feature is important as most energy storagetechnologies typically reduce in voltage over time and being able tooperate over a wide and low voltage range can increase the time periodover which the unit may operate before the energy storage element isrecharged or replaced.

FIG. 6 Shows another embodiment of a sense circuit. This embodiment usesa specific microcontroller 602, a PIC16F506 manufactured by Microchip®Inc. Similar implementations are possible using microcontrollers ormicroprocessors from other manufacturers. The PIC16F506 has an internalcomparator which can be used to replace the external comparator (Comp)502 in FIG. 5. This allows a significant reduction in size and cost ofthe system. The basic oscillator circuit is the same as FIG. 4 and thesame component values may be used. Instead of connecting the biasresistor R1 to the positive supply, it is connected to a digital outputfrom the PIC (bias). This output could be configured as any of thedigital outputs available, for example RC0. The PIC can source up to 25mA so supplying the 15 μA is well within its capability. This allows thePIC to switch off the bias when the oscillator is not being used,thereby providing a significant reduction in power consumption. A singlerelay 604 is used to switch the Mains and also switch the coil. Asuitable relay 604 is the Panasonic DE2BL2-3V. This relay 604 has twocontacts, (x1, x2). In the ‘set’ state contact (x1) is connected andcontact (x2) disconnected; in the ‘reset’ state contact (x1) isdisconnected and contact (x2) is connected. The relay 604 has two coils(y1, y2). When a pulse (of 2.25V to 3.75V and around 10-100 ms duration)is applied to y1, the relay 604 enters the ‘set’ state. When a similarpulse is applied to y2, the relay 604 enters the ‘reset’ state. Therelay 604 latches in either the set or reset states and can remain thereindefinitely. This has the advantage that the relay 604 consumes nopower, except for the very short instants when it is switched. Thismeans that the relay 604 generally does not add to the power consumptionin the ultra low power state. Contact x1 is placed in series with themains live input line which feeds the wireless power system and is usedto disconnect the mains when the system is in ultra low power mode.Contact x2 is used to replace switch SW3 404 in FIG. 5 and is used toswitch in the coil when the system is in ultra low power mode.

In one embodiment, the MPU 406 ensures that its power supply is notdepleted. A simple method of determining the available power is tomeasure the input voltage as this typically reduces as the energy isdepleted. This can be achieved by powering the MPU 406 directly off theEnergy Storage Element 204. In the PIC16F506 there is an analogue todigital converter (ADC) which is referenced to the input voltage supply.There is also a 0.6V reference voltage internally generated forcalibrating the ADC. By configuring the ADC to read the 0.6V referenceit is possible to determine the voltage of the power supply. Forexample, the PIC16F506 operates down to 2V power supply, but typically asupply of 2.6V is used to ensure reliable operation of the oscillator.Therefore, for example, a threshold of 2.8V may be appropriate fordetermining an undervoltage condition. The ADC converter has 8 bits (256levels), so at a power supply of 2.8V, the 0.6V reference should read(0.6/2.8)*256=54. If the reading goes above 54, then it is an indicationthat the power has dropped below 2.8V. If the system has a rechargeablebattery then it can power up for a period of time to recharge it when anundervoltage condition is determined. If the system does not have arechargeable battery then it can simply light an LED to inform the userthat the battery needs replacing. In either case the system may bepowered on during an undervoltage condition so that the wireless powerunit 200 continues to operate.

In one embodiment, if the MPU 406 employs a voltage regulator on itspower supply (e.g. if the Energy Storage unit 204 has a widely varyingoutput voltage), then the undervoltage condition may be determined byusing two low tolerance resistors (typically 1% or less) to form apotential divider across the Energy Storage 204 output voltage. If thereare no available input pins on the MPU 406 then the bias network (R1,R2) can be used. The exact bias voltage is not critical for theoscillator 402 so the bias resistors could be connected to EnergyStorage 204 output rather than the regulated voltage (the ratio of R1and R2 may be adjusted). When the oscillator 402 is switched off (byswitching off the comparators 502, 602), the noninverting input can betemporarily reconfigured to be an analogue input so that the biasvoltage can be read.

The relay 604 is controlled by digital outputs OP1 and OP2 from the MPU406. The digital outputs control transistors Q1 and Q2 to selectivelypulse either y1 or y2. These could be configured to be any of thedigital output pins available. For example, OP1 could be configured asRC1 and OP2 could be configured as RC2. In the current embodiment, thedigital output pins are not able to source or sink sufficient current toactivate the relays. External transistors may be employed. MOSFETs,JFET, or another type of transistor may be employed. In one embodiment atransistor with a very high off-resistance is selected to minimize thecurrent consumption when the relays are not being switched. NMOS devicesare used in this example, but PMOS devices may also be used. (PMOSdevices can allow the relay coils to be ground connected which canimprove reliability, an example of which is illustrated later in FIG.13). Diodes D1 and D2 are used to provide a return path for any back emfgenerated in the coil. OP1 is coupled to the gate of transistor Q1 andOP2 is coupled to the gate of transistor Q2. The sources of Q1 and Q2are connected to ground. The drain of Q1 is connected to coil y1 and thedrain of Q2 is connected to y2. The common connection between the twocoils is connected to the positive supply. In addition there is anoutput port for transmitting information to the main processor and aninput port for receiving information from the main processor.Alternatively a single bidirectional port can be used.

FIG. 7 illustrates by example how the ultra low power circuit 700interacts with the main wireless power circuit 704. The ultra low powercircuit 700 includes the Energy Storage Unit 204 and the Sense Circuit206. The Sense Circuit 206 includes a microprocessor, referred to as theULP processor 702 in this embodiment. The main circuit 704 includescomponents for wireless power transfer (in this example the mainprocessor 706, switch SW1 202, the mains rectification 218, DC/DCconverter 216, Inverter 210, resonant capacitor 214 and primary coil212). The ULP circuit 700 is continually powered on (though can be in‘sleep’ mode when not actively performing functions). The main circuit704 is controlled by the ULP circuit 700 and only powered on when theULP circuit 700 activates SW1 202. The output port of the ULP processor702 (SigU) is connected to an input port of the main processor 706 andan output port of the main processor 706 (SigM) is connected to theinput port of the ULP processor 702.

FIG. 8 shows an example state machine executed by the ULP processor 702in one embodiment of the wireless power supply. After initialisation,the ULP processor 702 starts in the Cal state (S1). In this state, theULP 702 processor measures the frequency of the oscillator of the sensecircuit so that subsequent measurements may be compared against it. Inalternative embodiments with different sense circuits this process maybe different or unnecessary. The Cal state generates the upper and lowerthresholds for frequency comparison. The system remains in the Cal stateuntil a valid calibration has been obtained.

After the Cal state (S1), the system switches the mains on and entersthe Power Up state (S2). It is possible that a device may have been puton the system just before the Cal state (S1) was executed, so the systemmay make a proper check for valid devices before engaging the ultra lowpower state. It takes time for the main circuit 704 to power up. Thestate machine therefore remains in the Power Up state (S2) until themain processor 706 asserts a high signal (SigM=1) on its output. Afterthis signal has been received the system initialises the Look Counter tox and enters the Look State (S3).

In the Look state (S3), the system waits for the main processor 706 todetermine if there is a valid device or not. If the main processor 706determines that there is no valid device (or that there is a foreignobject present) then it takes the signal low (SigM=0). The Look Counteris decremented each time this state is executed. The system remains inthis state until either the main processor 706 asserts a low signal(SigM=0) or the Look counter has reached zero indicating that it hasexecuted this state more than x times. If SigM=0 then the system entersthe Power Down state (S4), otherwise the system enters the Operate State(S6).

In the Power Down State (S4), the ULP processor 702 waits for the maincircuit 704 to determine that it is safe to power down the mains. Themain circuit 704 powers down all the components in an orderly fashionand waits until the coil voltage has reached a value close to zerobefore asserting SigM=1. After determining SigM=1, the ULP processorswitches the Mains off and enters the Ultra Low Power State (S5).

In the Ultra Low Power State (S5), the ULP processor 702 powers up thesense circuit oscillator, measures the frequency and powers down thesense circuit oscillator. If the frequency is outside the thresholdlimits determined by the Cal State then the system switches on the Mainsand enters the Power Up State (S2). Until that happens the systemremains in the Ultra Low Power State (S5).

If the system enters the Operate State (S6) from the Look state (S3),then it is because the main processor 706 determined that there was avalid device present and no foreign objects present. The main circuit704 therefore activates all the circuits to supply power to the device.The system remains in the Operate State (S6) until the Main Processor706 asserts (SigM=1). When SigM=1, the system switches off the Mains andenters the Power Reset State (S7). This indicates that either the devicehas become fully charged or that it has been removed. After either ofthese events it may be possible to start again with a new calibrationvalue.

In the Power Reset state, the Main processor 706 switches off theelements of the Main circuit 704 in an orderly fashion, waits for thecoil voltage to become close to zero and then asserts SigM=0. When theULP processor 702 determines that SigM=0 it enters the Cal State (S1).

The Power Reset state is similar to the Power Down state, except thatinstead of exiting to the Ultra Low Power State (S5), it exits to theCal State (S1). Instead of having an extra state (S7) it is possible touse an extra variable set by the Look State which indicates whether thestate after the Power Down state (S4) should be the Cal State (S1) orthe Ultra Low Power State (S5).

A false trigger may occur if the system has drifted (for example becauseof oscillator drift or because of ambient temperature fluctuation). Inorder to prevent the system getting stuck in a loop whereby itcontinually powers up and goes back to Ultra Low Power, it is possibleto have a limit on the number of ‘False Triggers’. This may beimplemented by having a False Trigger Count which increments every timea False Trigger occurs. A counter may be used to count each state andwhen this counter overflows (e.g. after 256 states) the False TriggerCount is Reset. After the False Trigger Count exceeds a certainthreshold, the system enters the Cal State (S1) so that a newcalibration can be obtained.

In addition, there is an Error State (S8), which can be entered from anystate if an error occurs. There a number of different causes that couldgenerate an error and only a few are listed here. This could begenerated by a timeout e.g. if a valid Calibration is not received aftera set number of state cycles or the Main Processor 706 does not assertSigM=1 to indicate it has powered up within a set number of statecycles. Once the error has been cleared, the system can enter the PowerReset state (S7), followed by the Calibration State (S1). Anundervoltage condition could also put the system into the error state.Alternatively there could be a separate state for the undervoltagecondition.

In one embodiment, the ULP processor 702 includes a main ULP processoroscillator clock and a separate watchdog ULP processor oscillator clockor timer. The ULP processor is configured such that it executes a stateafter every timeout of the watchdog timer. After executing theinstructions associated with each state, the ULP processor 702 is putinto a low power ‘sleep’ mode. In this configuration the ULP processoris temporarily suspended and all functions powered down where possible,including the main ULP processor oscillator clock. The watchdog ULPprocessor timer remains active while the other ULP processor functionsare suspended. The power consumption in sleep mode is specified to beless than 1.2 μA at 2V and is typically 100 nA. The time intervalbetween each state is a compromise between maximising the time theprocessor is in sleep to conserve power and having the time intervalshort enough that there is little observable delay. A suitablecompromise is to set the time interval to be nominally 288 ms byappropriate setting of the Watchdog prescaler.

FIG. 9 shows some example timing diagrams for a state machine of theform shown in FIG. 8. These show the signal SigU from the ULP processor702 and the signal SigM from the main processor 706. Initially thesystem is in the ULP state (S5). On the first state (1 in the diagram)the ULP circuit 700 detects that an inductance change has occurred andswitches on the mains and sets SigU=1. The ULP circuit 700 enters thePower Up state (S2). On the next 2 state transitions (2,3), The maincircuit 704 is still powering up and so SigM=0. Between the third andfourth transition, the main circuit 704 has fully powered up and setSigM=1. The main circuit 704 now starts looking for devices. On thefourth transition the ULP processor 702 sees that SigM=1, so itacknowledges by setting SigU=0 and then it enters the Look State (S3).During the Look state, the ULP processor 702 counts the state cycles.

If the main processor 706 determines that there is no device presentthen it sets SigM=0. If this occurs within a fixed number of statecycles (e.g. 5 or 10) then the ULP processor 702 determines that therewas no device present. In the example the main processor 706 sets SigM=0between the fifth and sixth transitions. On the sixth transition the ULPprocessor 702 sees that SigM=0 indicating that the main processor 706wishes to power down. The ULP processor 702 signals SigU=0 (to indicatethat it is working properly and ready to take over) and then enters thePower Down State (S4).

After the main processor 706 has received the acknowledgement from theULP processor 702 on the sixth transition it starts to power down allthe circuits in an orderly fashion. When this has been completed itwaits for the coil voltage to fall below a threshold value (typicallyclose to 0V) and then sets SigM=1. When the ULP processor 702 receivesthis signal (on the eighth state) it then switches off the Mains andenters the ultra low power state (S5).

If there had been a device present, then instead the main processor 706would have kept SigM=1 rather than setting SigM=0 between the fifth andsixth states. This would have meant that the number of cycles countedduring the Look state would have exceeded the threshold and the ULPprocessor 702 would have determined that a device was present andconsequently it would enter the Operate State (S6). The ULP circuit 700would remain in the Operate State until it received SigM=0 upon which itwould enter the Power Reset State (S7).

The software to implement the state machine can be written directly inthe assembly language of the MPU or it can be written in a higher levellanguage (for example C) and compiled to assembly language or a hybridof the two can be used. It is advantageous to use assembly language toimplement the measurement function as it means that only a single 8-bitcounter is required. The measurement can be made over a time intervalfixed by a set number of instruction cycles executed by the MPU. The MPUcan periodically check to see if the counter has overflowed andincrement an overflow counter byte if this happens (taking care toensure that this branch does not alter the time taken). The measurementtime interval is a trade off between having high sensitivity andensuring that the MPU is in sleep mode for most of the time. A suitablecompromise is 1 ms, but shorter or longer periods may be used. The PICmay be configured to use the internal 4 MHz oscillator to give low powerconsumption whilst allowing accurate measurements to be made.

The calibration routine may set the upper and lower thresholds in orderto trigger the Sense Circuit 206. The number of periods counted duringany particular measurement period will typically vary by one dependingon the phase of the oscillator 402 with respect to the phase of theinternal clock at the time the measurement is made. It is possible tomake a series of measurements for the calibration routine (e.g. 5 or 10)to determine the highest and lowest counts. The Lower Threshold can thenbe set to be a fixed number of counts (e.g. 2) below the lowest readingand the Upper Threshold can be set to be a fixed number of counts aboutthe highest reading.

Before each measurement or series of measurements the oscillator 402 andbias circuit may be turned on. This is achieved by switching on thecomparator 502 and switching on the port to apply the bias. Likewisethese should be switched off after each measurement or series ofmeasurements.

It is possible to conserve power in the ultra low power mode as thesystem will likely be in this mode for the vast majority of the time.The amount of time it takes for the oscillator 402 to wake up andstabilize may vary from device to device and over time and temperature.Rather than wait for a set period of time (which may include some extramargin) it is possible to reduce the time the oscillator 402 is switchedon for to conserve power. A number of measurements are taken in a loopand this loop is exited early if the measurement falls between the Upperand Lower thresholds. It is unlikely that random noise will result in ameasurement between the two thresholds (even if this does occur, thesystem will trigger on the next state transition if an inductance changehas taken place). For example, a series of seven 1 ms measurements aretaken and the loop exits on the first valid measurement. Using thistechnique, the total measurement time to make a decision is typically 2ms (because the oscillator generally starts up in less than 1 ms). Thisresults in extremely low power consumption during ultra low power,because the MPU 406 and oscillator 402 is only active for 2 ms eachstate transition. If the time between state transitions is 288 ms, thenthe MPU 406 is in sleep mode (with oscillator off) for 99.3% of thetime. Using a PIC16F506, the power consumption of the system in ultralow power mode is typically only around 30 μW. This means thatnon-rechargeable batteries (e.g. 2×AA or 2×AAA alkaline cells) could beused as the lifetime would be a number of years.

Although the example shows a synchronous state machine, whereby there isan equal time interval between each state, it is possible to use anasynchronous state machine, or to use an alternative implementationwithout a state machine. The state machine or algorithm could beimplemented in hardware, in an application specific integrated circuit(ASIC) in a field programmable gate array (FPGA) instead of amicroprocessor.

Instead of communicating between the ULP processor 702 and the mainprocessor 706 as described, the processors could communicate morecomplex messages using a serial or a parallel link. They could use astandard such as an I2C bus. The ULP processor 702 could communicateinformation to the main processor 706 relating to the measurements made.This could enable the main processor 706 to deduce information about thedevices. For example from the inductance change measured, the mainprocessor 706 could deduce that the device is of a particular type andtherefore adapt its frequency and/or voltage/current/power levelsaccordingly. This could allow a faster start-up as it would avoid theneed to send multiple pings of different frequency to establish thedevice type. The frequency could be adapted by varying the frequency ofthe signal applied to the coils and/or varying a capacitance and/orinductance to change the resonant frequency of the system. The systemcould alternatively, or in addition to, use the knowledge of theabsolute frequency of oscillation to establish the resonant frequency ofthe system directly.

There are numerous other oscillator circuits that may be used instead ofthe LC comparator oscillator. For example and without limitation,oscillators based on JFETs, bipolar or MOSFET transistors, operationalamplifiers or logic gates may be used. Various oscillator topologiesincluding without limitation Hartley, Clapp and Armstrong may be used.Rather than measuring the inductance of the primary coil 212, a separatecoil may be used for sensing the presence of a device or other object.

Instead of using 2-coil latching relays, it is possible to use a singlecoil latching relay. This may allow a cost reduction as the relay hasonly one coil instead of 2. Such a relay requires a short (˜5 ms) pulseof current in one direction to ‘set’ it and a pulse of current in theopposite direction to ‘reset it’. Such a relay can be driven by using 4MOSFET transistors in a bridge configuration. FIG. 10 shows a singlecoil relay driven by two complementary MOSFET pairs Qa, Qb, Qc, Qd (theresistors Ra, Rb, Rc and Rd are not required for driving the relay). IfA and B are both low (0) then no current flows. Likewise if A and B areboth high (1). However if A=1 and B=0 current flows in one direction(e.g. ‘set’). Conversely if A=0 and B=1 current flows in the oppositedirection (e.g. ‘reset’). By applying a pulse to A, the relay will latchin the ‘set’ state and by applying a pulse to B, the relay will latch inthe ‘reset’ state.

A low specification MPU 406 may be used so as to reduce both cost andsize. By novel multiplexing of the pins it is possible to use an 8-pinPIC12F510 instead, saving cost. The separate I/O port for the bias canbe eliminated by combining it with the two ports required to drive therelay. In FIG. 10 the four resistors Ra, Rb, Rc and Rd are used forsupplying the bias to the oscillator 402. By example, they could each be100 k Ohm resistors. The presence of these resistors does not materiallyaffect the operation of the relay drive. If A=1 and B=0 current flowsthrough the relay in one direction and in the opposite direction for A=0and B=1. No current will flow through the relay if A=B=0 or if A=B=1.However if A=B=1, Vbias will nominally be at half the supply voltage andif A=B=0, Vbias will be nominally 0V. This enables a convenient way ofswitching the bias to the oscillator 402 on and off without the need fora separate I/O port. The resistors should be relatively well matched toprevent extraneous current. Rc and Rd could be replaced by a resistortwice that of Ra. Although extra current flows through the resistorswhen the relays are switched, the pulses are very short and the extracurrent (˜15 μA) is negligible compared to the current through the relay(typically 50 mA).

The output port for the ULP processor 702 to communicate with the Mainprocessor 706 can be multiplexed with the comparator output pin used forthe oscillator 402, 602. When the oscillator is running, the mainprocessor 706 will generally be switched off so there may be no need forthe output port to be enabled during this time. FIG. 11 shows animplementation of the system using a PIC12F510 and a single coil relay,using the bias configuration of FIG. 10 (using the same labels).

The use of a single relay for switching both the Mains and the Coiltogether can be advantageous for saving cost. However a drawback is thatthere can be extra time delays between powering up and powering down.This will be evident after a calibration has been performed and thesystem powers up to check for devices before going into ultra low powermode. An alternative is to use two separate relays, one for the coil andanother for the Mains. This means that it is not necessary to powereverything down when performing a calibration. An alternative is to usea single relay, but hold up the power to the main processor 706 (forexample with a capacitor) so that it remains powered up whilst the Mainsis switched off momentarily for the calibration.

FIG. 12 shows an alternative embodiment of the invention in which theultra low power system is ‘retro-fitted’ as an aftermarket accessory.This could be used to upgrade wireless power systems from the samemanufacturer or from a different (third-party) manufacturer. Optionallythe wireless power system may be designed to enable easier upgrading inthe future. In FIG. 12, the DC power supply used to supply DC power tothe wireless power supply 1214 is replaced with the ‘Replacement DCPower Supply’ 1202. The Replacement DC power supply 1202 has a mainsinput socket, fuses, an EMI/RFI suppression filter on the input. TheLive terminal is routed via the Mains Relay 1206 to the input of aswitch mode power supply 1210. Optionally the Neutral terminal can berouted via the relay or it can be wired to the power supply directly.The output 1212 of the power supply 1210 is regulated via a voltageregulator LM317 which also has overload and short circuit protection.The output of the regulator goes through a negative temperaturecoefficient thermistor (NTC) 1216 to the DC power output socket 1222. Itis possible that the wireless power supply 1214 will have a large inrushcurrent generated when the device is powered up. This is a large spikeof current (maybe as high as 20 A or more) for a short period of timeand may be caused by charging up large capacitors present across thesystems power rails. The NTC thermistor 1216 is a resistor which reducesin resistance when it heats up. The thermistor limits the current whenthe mains is first switched on and then heats up so that it has lowlosses during normal operation. A value of around 10Ω may beappropriate.

As well as the DC power socket 1222 there is also a control socket 1224(these two could be combined so that only a single cable is required).The contacts for the relay 1206 (Coil1, Coil2 and Coil Comm) are routedto the control socket 1224. Also present are two AA cells 1208, theterminals of which are also routed to the control socket 1224. The AAcells 1208 could be located in a battery compartment which is accessiblewithout exposing other connections (for example the live mains) in theReplacement DC Power Supply 1202. The AA cells could be primary orrechargeable cells.

The DC power socket 1222 is connected to the existing power input socket1218 on the wireless power supply 1214. The control socket 1224 isconnected to the ULP circuit, an example of which is shown in FIG. 13.The ULP circuit has a Sense Circuit 206 similar to that of FIG. 6.However, in this configuration there is a second relay 1306 used toconnect and disconnect the coil from the sense circuit 206 (the firstrelay 1206 being located in the replacement DC power supply). A smallsurface mount single coil relay is used (Axicom IM41GR). The circuitconnects to the coil terminal, the ground terminal and an output fromthe main processor 706 which indicates a ‘Valid Device Present’ signal.The ‘Valid Device Present’ signal should only be active when there is adevice receiving power or ready to receive power (as opposed to a fullycharged device present or an object not configured for receiving powerpresent). This Valid Device Present signal could be an output from themain processor 706 which is used to control an LED output (for examplethe wireless power supply may illuminate an LED when a device ischarging). The system could be retrofitted to the circuit board bysupplying a kit which the user solders to the existing board.Alternatively the user could have the operation performed by sending theunit back to the manufacturer or retailer.

The wireless power unit may be designed for future upgrading by routingthe pins on the main circuit board out to a socket 1220. The circuit canbe very small and therefore actually integrated into a plug whichconnects to this socket on the main circuit board 704. The socket couldbe positioned and designed such that there is no unsightly protrusion.Optionally I/O pins may be routed from the main processor 706 to thesocket so that the full communication between the main processor 706 andthe ULP processor 702 is possible enabling a control system like the oneillustrated in FIG. 8 to be implemented. There may also be a connectionto enable the main processor 706 to determine if an ultra low powersystem is present so that it can execute different software code if oneis present. Alternatively a retrofit operation would also involve are-programming (re-flashing) of the main processor 706 software to adaptthe code for ultra low power operation.

If the wireless power system has not been designed for future upgrading,then the ULP processor 702 can implement a state machine similar to theone in FIG. 14. The system starts in the Calibration State 1402. Acalibration measurement is made and used to determine the upper andlower measurement thresholds for triggering an inductance change. Aftera valid calibration measurement has been made the system enters the Pingstate 1404. The system remains in the Ping state for a set period oftime, determined by decrementing a Ping counter on each statetransition. After the Ping counter has reached zero, the system moves tothe Ultra Low Power state 1406 if Device Present=0. If, however, DevicePresent=1, the system moves to the Operate state 1408. The countershould be set such that there is sufficient time for a device to bedetected and the Device Present output enabled.

In the Ultra Low Power state 1406, the system measures the inductance oneach state transition. It remains in this state until a measurement ismade which is outside the upper and lower thresholds set by theCalibration state 1402. When such a measurement is found, the Falsetrigger count is decremented and if it has not reached zero the systementers the Ping state 1404. If the false trigger count reaches zero, thesystem enters the Calibration state 1402. The false trigger counter isperiodically reinitialised.

In the Operate state 1408, the system looks at the Device Present pin oneach state transition. The system remains in the operate state 1408until Device Present=0 and then moves back to the Calibration state1402.

If the wireless power system encounters an error, the system moves tothe error state 1410 until the error is cleared, at which point thesystem moves to the calibration state 1402.

FIG. 15 shows an embodiment in which the existing DC power supply 1502is retained. Instead there is a Mains switch 1504 which is retrofittedbetween the mains socket and the mains input of the existing wirelesspower supply system 1508. This system can be used if the existingwireless power unit 1506 has an integral DC power supply 1502 or if theDC power supply is a separate unit (not shown). The Mains switchincludes the mains relay 1206, the energy storage element 1208 and aconnector for the control cable. The control cable connects to aseparate Sense/Control circuit 1510 which is retrofitted to the existingwireless power supply 1506.

The Sense/Control circuit 1510 includes a ULP circuit, for example theULP circuit shown in FIG. 13. Alternatively The Sense/Control circuit1510 could be completely independent and not require any connection tothe main circuit as described in later embodiments. For example aseparate proximity detector may be used. This is particularly convenientfor retrofitting third-party systems where the main circuit is notaccessible.

If there is no Device Present pin available, the control circuit cansimply switch the mains on when there is a device detected by theproximity detector and off when there is no device detected.

Two relays may be used in the retrofit example so that the oscillatorcircuit has relatively short leads to the primary coil. This enables theAC resistance to be reduced to ensure reliable oscillator operation. TheMOSFETs for the mains relay 1206 could alternatively be located withinthe replacement power supply.

FIG. 16 shows one implementation of the Energy Storage Unit 204 in whichthe energy storage unit can be recharged from the main circuit 704. TheEnergy Storage unit 204 takes DC power as its input. This is coupled toa charge controller 1602 which supplies power to an energy storageelement 1604. The energy storage element 1604 is optionally asupercapacitor, but other elements may be used such as a battery orother form of electrical energy storage. One form of charge controller1602 that may used is a Buck regulator in which the output capacitor isreplaced by the supercapacitor. Feedback is used to drive the Buckregulator such that constant current is delivered to the supercapacitor.The energy storage element 1604 is coupled to the Energy Storage Unitoutput. There may also be protection circuits 1606 and/orvoltage/current regulation/limitation 1606. In one embodiment there isalso an output which is indicative of the energy level of the energystorage element 1604.

In the this embodiment, the Energy Storage element 1604 is monitored sothat it does not deplete fully, preventing operation of the SenseCircuit 206. This may be charged from the power input when the Wirelesspower supply is delivering power to the load. In addition, the SenseCircuit 206 periodically monitors the energy in the Energy Storageelement 1604 via the Energy Level Output from the Energy storage unit204. If this gets below a certain threshold, the Sense Circuit 206activates SW1 202 so that the Energy Storage element 1604 can berecharged.

FIG. 17 shows an Energy Storage unit 204 in which there is additionallya diode 1702 to prevent back feed of current into the chargingcircuitry. There is also a switch 1704 in this embodiment. The switch1704 may be opened when the Sense Circuit 206 is being powered from theEnergy Storage Unit 204 to prevent reverse leakage current fromdepleting the capacitor or cell. Instead of using a rechargeable EnergyStorage unit 204, it is also possible to use a non-rechargeable primarycell. In this case, a battery compartment with a removable cover is usedso that the battery or batteries may be removed when they are exhausted.

FIG. 18 shows an example flow diagram illustrating the operation of anultra low power system. The system first checks 1802 the energy level inthe Energy Storage element. If it is low then the mains is connected1810 and power supplied 1812 to it to recharge it. If the Energy is notlow then the mains is disconnected 1804 to reduce power consumption. TheSense Circuit 206 then sees if there has been an inductance change 1806.If there has not, then after a period of waiting 1808, the system goesback to the start 1800. If there has been an inductance change, thesystem connects 1814 the mains and sees if the there is a devicerequiring power 1816. If there is not it goes back to the start 1800. Ifthere is, the system checks to see if there is a foreign object present1818 (this may have been placed at the same time as the device). Ifthere is then the system goes back to the start 1800. If there is not,then the system delivers power to the primary coil 1820 to supply powerto the portable device. It continues to check that the device is stillrequiring power 1816 and only goes back to the start 1800 when thedevice no longer requires power or if a foreign object 1818 is placed onthe wireless power supply.

In some embodiments, the primary unit makes a determination aboutwhether a valid secondary device is present and whether a secondarydevice desires power. It should be understood that these determinationscould be made simultaneously or at different times. For example, if thesecondary device sends a request for power, that may be interpreted toindicate both that a valid secondary device is present and that asecondary device desires power. Further, to the extent that a secondarydevice desires power, it should be understood that the secondary deviceneed not issue a request for power, or be low on power, in order todesire power. For example, the secondary device that wishes to receive atrickle charge may still be characterized as desiring power.

FIG. 19 shows one embodiment of a method for implementing the system inwhich there are two power states. In the first mode, A, 1902 the systemis in the equivalent to the ultra low power mode described above 1906.In this state the Sense Circuit 206 is powered from the Energy StorageUnit 204. If the Energy Storage Unit 204 gets low 1908, then the systempowers up the mains 1910 to recharge it. The Sense Circuit 206periodically looks for a change 1912 indicating a device or object mayhave been placed on or removed from the charger. If the Sense Circuit206 detects that a change has taken place then the System enters state B1904.

In mode B 1904, system is connected to the mains. The systemperiodically ‘pings’ 1914 the system by modulating the primary coil, Lp.If there is a portable device present then it replies (e.g. bymodulating its load). If the system detects 1916 that there is a validdevice then after checking that there are no foreign objects present,the system will deliver full power to the primary coil 1920. The systemwill keep sending a ‘ping’ for a predetermined number of ‘pings’ or apredetermined amount of time 1918. These predetermined numbers may besoftware configurable (and/or dynamically variable). If no device isdetected during this time then the system will go back into state A1902.

One advantage of this arrangement is that it gives more opportunity tocheck if there is a valid device present. This prevents the systemremaining in standby indefinitely if there is a valid device on it thatwas not detected on the first ‘ping’. Some portable devices take time to‘wake up’ The first ‘ping’ may deliver sufficient power to start-up themicroprocessor. However it may take longer to ‘boot up’ than the ‘ping’duration. Such a device should then authenticate on the second ‘ping’.

FIG. 20 shows an exemplary timing diagram to illustrate the method ofFIG. 19. FIG. 20( a) shows the system when a foreign object is place onthe system. The system starts in mode A 1902. It sees an inductancechange and then goes into mode B 1904 for three ‘pings’. These ‘pings’can be of a different time interval to the polling of the Sense Circuit206. As no device is detected, the system goes back to mode A 1902. FIG.20( b) shows the system when a valid device is placed on the system. Inthis example, the device does not authenticate on the first ‘ping’, butit is able to on the second ‘ping’.

If the Energy Storage unit 204 requires a relatively long time torecharge, then instead of powering up for a quick charge (for example ifthe Energy Storage unit 204 is a battery such as a Li-ion battery), thenthe example flow diagram of FIG. 21 could be used. In this flow diagramthe system leaves sleep mode 2002 with the mains disconnected 2006 andenters Mode B 2004 if the Energy Storage unit 2004 falls below a setthreshold 2008 or the coil state changes 2010. The system remains inMode B 2004 until there are no devices requiring charge 2012, 2014, 2016and the Energy Storage unit has been fully charged 2018, 2022, 2020.

FIG. 22 shows an alternative embodiment in which the energy storage unit204 is also used to power the main circuit 704 for a period of time. Inorder to reduce the time delay between the device triggering the systemand the system powering up, the system uses the Energy Storage element1604 as a temporary source of power. Once the Sense Circuit 206 istriggered, the mains is switched on. The system then connects the EnergyStorage element 1604 to the main circuit 704 to power up the variouselements. This allows the system to authenticate the device whilst themains power is still powering on. The energy required to authenticate adevice may be less than that required to deliver power. Optionally, ifthe Energy Storage element 1604 is of sufficient capacity to deliverpower, the system may also supply power from the Energy Storage element1604 to the device. Once the mains has powered up along with all theother supplies, the system switches over so that it is fully poweredfrom the mains. The system can then also supply power to the energystorage unit 204 in order to recharge it.

FIG. 23 shows an alternative embodiment in which a single processor 2302is used instead of separate processors for the ULP circuit 700 and themains circuit 704. In this arrangement, the processor 2302 would onlypower up the elements that it requires at any particular time. Thesingle processor 2302 could be powered from the Energy Storage element1604 continually, or alternatively it could switch its power input tothe mains generated one if it is powered up. In order to conserve power,the single processor 2302 could ‘switch’ clocks so that it runs at alower clock speed in ultra low power mode. This embodiment mayadditionally use the energy storage unit 204 to supply power to deviceswhilst it is waiting for the mains to power up. The single processor2302 configuration could be used to implement all the embodiments inwhich two or more processors are used. This includes deducinginformation about the device from the inductance sensing and using thisinformation subsequently, such as identifying the type of device andappropriately adjusting frequency and voltage.

The processor may be configured to be a dual core (or multi-core)processor. The two cores may run independently of each other. One core(the Main core) is used for the main wireless power circuit and theother core (the ULP core) is used for the ULP functionality (such as thesense circuit and control of the Relays). Some or all of the sensecircuit may be incorporated into the ULP core (e.g. comparators for theoscillator circuit and other passive components). The main core may bepowered down when in ULP mode and the ULP core may be powered down inoperating mode. During transition periods, both cores may be powered.The ULP core may take its power exclusively from the energy storage unitor it may take its power from a combination of the mains circuit and theenergy storage unit or it may take its power only from the mainscircuit. The ULP processor may be optimised for lower power consumptionthan the main processor (e.g. by running at a lower clock speed). TheULP core may be isolated from the main core (e.g. by etching trenches ordepositing insulating material) in order to minimise current leakage.

A number of different processors and control units are describedthroughout the various embodiments. The FIG. 2 embodiment includes acontrol unit 208 and a sense circuit 206 that includes an integratedmicroprocessor, for example as shown in FIGS. 4-6. The FIG. 7 embodimentincludes a ULP circuit with a ULP processor separate from the sensecircuit. The sense circuit may or may not have its own microprocessor inthe FIG. 7 embodiment. The FIG. 16 embodiment of the energy storagedevice includes a charge controller. As just discussed, the FIG. 23embodiment includes a single processor and the sense circuit does notinclude a processor. The FIG. 26 embodiment includes a microcontrollerunit that has includes a digital oscillator output and an analogue todigital (A/D) input. It should be understood that the number andfunction of the microprocessors may be spread out in essentially anymanner that enables the appropriate control functions to be powered upand available at the appropriate times. To the extent that there are anysubstantive differences introduced by the introduction of differentterminology, such as processor, microprocessor, MPU, MCU, PIC, ULPprocessor, charge control, charge unit, or any other controllerterminology, these differences in terminology should not be read tolimit the scope of the invention. Instead, it should be understood thatthe controller locations and schemes may be exchanged among theembodiments.

Instead of measuring the frequency of an oscillator 402 to implement theSense Circuit 206, there are numerous other techniques that may beemployed. FIG. 24 shows an alternative implementation of the SenseCircuit 206. In this arrangement, the Sense Circuit 206 uses the samecoil for detection as used for the transfer of power, Lp 212. The SenseCircuit 206 has an additional inductor Lsen 2404, which forms a bridgewith the primary coil, Lp 212. (Although an inductor is used anyimpedance: resistive, reactive or a combination of other elements may beused), This bridge may be driven with an Oscillator 402. In thisembodiment, the oscillator output voltage and frequency is such thatthere is minimal power dissipation across the inductance bridge formedbetween Lsen 2404 and Lp 212. If the inductance seen across Lp 212changes, then this will result in a change in the peak voltage at themidpoint of the bridge, M. This inductance would change if a portabledevice, such as that shown in FIG. 1 was placed on the wireless powersupply 200, such that the secondary coil coupled to the primary coil.This would be true whether or not there was a load in the portabledevice. The inductance would also change if a metal object or an objectcontaining magnetic material was placed in proximity to the primarycoil, Lp 212. Likewise the inductance would change if a device or metalobject was removed from the wireless power supply 200.

In this embodiment, the Sense Circuit 206 detects the peak voltage atpoint M using a Peak Detector 2402. The output of the Peak Detector 2402is fed into a microprocessor unit (MPU) 406. The MPU 406 periodicallyreads the value of the peak detector 2402. If this value changes,between two consecutive readings then the Sense Circuit 206 determinesthat an inductance change has occurred, and the Wireless power supply200 checks if there is a valid device requiring power or whether this isdue to a foreign object. It may perform a running average on themeasurements to reduce the effect of noise.

The sense circuit 206 may use two switches controlled by the MPU 406,SW3 404 and SW4 408. In the illustrated embodiment, SW3 404 is used toisolate the Sense Circuit 206 from the primary coil, Lp 212 whenwireless power supply 200 is delivering power to the portable device.Switch SW3 404 is closed during standby mode and open during powerdelivery. Switch SW4 408 is used to reduce the power consumption of theSense Circuit 206 still further. Rather than have the Oscillator 402 andPeak Detector 2402 powered continuously, the MPU 406 only closes SW4 408for the duration of each inductance measurement. Although SW3 404 iscontrolled by the MPU 406 within the Sense Circuit 206 in this example,it may instead be controlled by the Control Unit 208 within the mainWireless Power Supply 200.

FIG. 25 shows a flow diagram illustrating one implementation of thesystem. This flow chart illustrates the separate measurements made todetermine the inductance change. In this variation, if the EnergyStorage element 1604 is depleted then the system temporarily does notuse the Sense Circuit 206, but only uses the device validation systemuntil the Energy Storage element 1604 is charged. In FIG. 25, X1 is thethreshold below which the Energy Storage element 1604 is recharged, X2is the threshold above which it is fully charged. Y is the difference ininductance measurements to trigger the Sense Circuit 206. In thisexample, the memory containing the inductance reading is updated aftereach measurement. This means that the circuit will follow drifts overtime, e.g. due to fluctuation in the coil inductance with ambienttemperature. Alternatively, the memory is not updated. This will meanthat there will be more false triggers due to fluctuation in ambientconditions. However, it will also prevent the system from being fooledif a device is brought very slowly into proximity with the system.

Referring now to FIG. 25, beginning at the start 2502 of the flowdiagram, SW1 is opened while SW3 and SW4 are closed 2504 so that thepeak detector can be read 2506 and stored into memory 2508. When themeasurement is complete, SW4 is opened 2510 and the amount of energy inthe energy storage element is measured 2512 and stored in memory 2514.If the amount of energy is not below the threshold 2516, then theprocessor waits 2518 and closes sw4 2520 to ready the peak detector 2522and store the value into memory 2524. Once the second peak reading istaken SW4 is opened 2526 and the absolute value of the two readings arecompared to a threshold 2528. If the comparison is below the thresholdthen there is not a large enough difference in the inductancemeasurements to trigger the Sense Circuit and the second measurementoverwrites the first measurement in memory 2530, 2532 before returningto read the amount of energy in the energy storage element 2512. If thedifference in inductance measurements triggers the Sense Circuit 2528 orthe energy storage element needs to be recharged 2376, then SW3 isopened and SW1 is closed 2534. The system determines whether a device ispresent 2536 and whether it needs power 2538. If no foreign object ispresent 2540 then power is delivered to the remote device 2542. After awaiting period, a waiting period 2544, the system checks to see if thedevice is still present, needs power, and that no foreign objects havebeen placed. If a device isn't present, doesn't need power, or if aforeign object is present, then the system checks if the energy storageelement is above its charged threshold 2546. The system will continue tocharge the energy storage element until it is above the threshold andthen return to standby 2504.

FIG. 26 shows one implementation of a sense circuit using amicrocontroller unit (MCU) 2602. The MCU includes a digital oscillatoroutput and an analogue to digital (A/D) input. In this implementation,the inductance of the primary coil, Lp 212 is used to form a bandpassfilter. This filter is used to selectively filter the fundamentalfrequency component of the square-wave signal to generate a sinusoidalone. However, as the inductance of Lp 212 changes, the passbandfrequency also changes, thereby altering both the amplitude and phase ofthe resultant signal. One advantage of this embodiment is that thefiltering and inductance detection are performed in the same step usingonly passive components.

In this embodiment, the digital squarewave output is AC coupled via C2to the parallel combination of Lp 212 and C1. Lp and C1 are resonant inthe vicinity of the oscillator frequency. This combination is then ACcoupled via C3 to a level shifter formed by R1 and R2. R1 and R2 add aDC component to the signal to prevent negative voltages entering theMCU. The top of R1 is fed with the rail voltage of the oscillator. Thisis provided from an output pin of the MCU 2602. This means that when ameasurement is not taking place that the MCU 2602 can remove thisvoltage and prevent power dissipation through R1 and R2. The output fromthe level shifter is applied to the analogue to digital converter inputof the MCU 2602.

Generally, greater sensitivity can be obtained at the expense of higherpower consumption, so there is a trade-off to be made. This could be forexample, using amplifiers, using phase sensitive detection rather thanpeak detection, using higher voltage levels, or having longeracquisition times and hence less time when the Sense Circuit 206 is insleep mode. It is possible to make this trade-off software configurable,so that depending on where the system is located, the sensitivity andpower consumption can be optimised.

The frequency of the oscillator signal in the Sense Circuit 206 maydynamically adapt. This could be to position the frequency on the mostsensitive part of the inductance versus output amplitude curve, or toposition it in a region of low power dissipation or to position it in anoptimised trade-off between the two. The frequency could be adapted atpower up, periodically or whenever the Sense Circuit 206 is reset. Forinstance when a device or metal object is placed on the wireless powersupply 200 it might take the Sense Circuit 200 close to the limit of itsdynamic range. The Sense circuit 206 could adjust the oscillator tobring it back to near the centre of the range when sensing for the nextevent. An alternative way of implementing the system is to always adjustthe frequency to the position of maximum amplitude. Any reduction inamplitude would then indicate that a change had taken place.

FIG. 27 shows exemplary operation of this circuit of FIG. 26. FIG. 27(a) shows a signal within the MCU 2602 (divided down from its internaloscillator clock). FIG. 27( b) shows the oscillator output from the MCU2602 which is applied to the impedance bridge. FIG. 27( c) shows thesignal at the midpoint of the bridge under one set of conditions. Thissignal differs in amplitude and/or phase. FIG. 27( d) shows the signalat the midpoint of the bridge under a different set of conditions (forexample if a device or metal object is placed on the wireless powersupply). In general FIG. 27( d) differs from FIG. 27( c) in amplitudeand/or phase. The microprocessor 2602 first allows the oscillator signalto settle. For each inductance measurement, a number of readings formthe A/D converter are taken at a specific number of clock cycles from agiven reference point, 0. These three reading points are labelled i, ii,iii in FIG. 27( a). The values read by the A/D converter at thesereading points are illustrated in FIGS. 27( c) and 27(d). It can be seenthat in this example the values obtained in the case of FIG. 27( d)differ to those of FIG. 27( c) indicating that some change has occurred.One advantage of sampling the signal at different points, rather thansimply measuring the peak signal is that the sense circuit 206 can bemade more sensitive because the circuit responds to changes in phase aswell as amplitude. In one embodiment, the measurement points do notcoincide with the same points in the cycle of the sense frequency. Inparticular at least one reading may be obtained which is of significantamplitude as comparing two values close to zero is prone to errorsinduced by noise. One way to ensure this is to make sure that the timeinterval is not constant (e.g. the time interval between reading i andreading ii is different to that between reading ii and reading iii).

The Sense Circuit 206 may be sensitive to phase, because it is possiblethat there is a change in impedance caused by the addition of ferrite orother similar material in the secondary coil which exactly balances theimpedance of the load. An alternative to making the Sense Circuit 206phase sensitive is to make two peak amplitude measurements at differentfrequencies as the inductive impedance has a different frequencydependence to the AC resistance losses.

FIG. 28 shows an alternative embodiment of the FIG. 26 implementationwhere a peak detector is used. Some MPUs do not have fast analogue todigital converters, making a phase sensitive technique impractical. Inthis example, the peak detector is formed by a diode, D1 2802 andcapacitor C4.

FIG. 29 shows an alternative embodiment in which phase-sensitivedetection is used. Capacitor C1 forms a bandpass filter with the primarycoil, Lp 212, similar to the FIG. 26 embodiment. There are also DCblocking capacitors C2 and C3 and the level shifter (R1, R2). However,the output from the level shifter is coupled to the input of theinternal comparator that the microcontroller 2902 of this embodimentemploys. The other input can be set using an internal reference midwaybetween the supply rails. This comparator is used to generate a cleandigital signal from the level shifter which will be sinusoidal andattenuated. The digital signal from the comparator is coupled to oneinput of a phase detector (Phase Detector) 2904, the other input comingfrom the oscillator output. The output of the phase detector 2904 iscoupled to an analogue input of the MCU. As the effective inductance ofthe primary coil 212 changes, the phase of the signal at the levelshifter will vary with respect to the oscillator output. The phasedetector 2904 has as an output an analogue voltage representative of thephase difference between signal relative to the oscillator output and istherefore a measure of the inductance.

The phase detector 2904 can be realised, for example, using a exclusiveOR gate 2906 coupled to a low pass filter, the low pass filter being aseries resistor 2908 and a capacitor 2910 to ground. Optionally, a phaseshifter 2906 can be used in either path to the phase detector 2904. Thiscan be used to bias the system so that the phase detector 2904 output ismidway between its range when the bandpass response is centred on theoscillator frequency. Then it is possible to distinguish betweenpositive and negative inductance excursions from the centre frequency.The phase shifter 2906 should provide 90 degrees of phase shift. Thismay be implemented by using two RC networks (2912, 2914, 2916, 2918) asshown at the expense of attenuating the signal. Rather than introduceextra attenuation into the signal path, an alternative is to phase shiftthe oscillator signal applied to the second input of the phase detector.In this case the signal may be converted to a digital signal using asecond comparator.

FIG. 30 shows a variation on the embodiment of FIG. 24. Instead of theSense Circuit 206 having a separate impedance (Lsen in FIG. 24), theSense Circuit 206 uses the resonant capacitor 214 in series with theprimary coil. The sense subcircuit outlined in FIG. 24 refers to thesense circuit in the current embodiment illustrated in FIG. 30. TheOscillator 402 is applied to the point at which the capacitor 814 isconnected to the inverter 210 output. The midpoint of the capacitor 214and inductor 212 is connected to the peak detector 2402. When a deviceis placed in proximity to the primary coil 212, the effective inductanceseen across the primary coil 212 will change, thereby changing theresonant frequency of the capacitor-inductor combination. This will inturn change the amplitude and/or phase of the signal at the peakdetector. An advantage of this embodiment is that it is unnecessary tohave an extra impedance element for the Sense Circuit′. However, it maymean that two switches 3002 are required to isolate the Sense Circuit′from the primary coil.

FIG. 31 shows an example of the invention when the wireless power supply200 has a DC input rather than a mains input. In this example, the DCPower Supply 3102 is located at the mains electricity outlet and a cable3104 delivers DC power to the wireless power supply 200 including thedrive/control unit 3106. The DC Power supply 3102 includes the MainsRectification 218 and a DC/DC converter 216. However, it also includes aswitch 3108 prior to the Mains Rectification 218. The cable 3104 betweenthe DC Power Supply and the Wireless power supply 200 includes anotherline so that the switch 3108 in the DC Power Supply 3102 can becontrolled by the Sense circuit 206.

The DC supply 3102 may be also be used without the Wireless power supply200, to power different equipment. Other equipment that has a DC powerinput may benefit from the DC Power supply 3102 of FIG. 31. Suchequipment would have an Energy Storage Unit 204 which powers a small MPU406 when it is in its standby state. Upon receiving a trigger signalfrom a stimulus, the equipment could signal via the cable 3104 to closeswitch SW2 3108. Such stimulus may come from a remote control signal(e.g. optical, wireless, RF, ultrasonic), or from a proximity sensor orfrom another piece of equipment, or from a timer etc.). Alternativelythe equipment may have a push button switch which activates SW2 3108without the need for a separate energy storage unit 1604 ormicroprocessor 406.

FIG. 32 shows one embodiment of a smart power supply 3120 with logic3202 controlling a similar process at the power supply 3120. This samepower supply 3120 may control voltage levels and the sleep cycle of thepower supply 3120. Such power supplies are used to power newer laptops.A simple command or logic level can control various aspects of the powersupply 3120 along with starting and ending a sleep cycle of much lowerpower drain.

FIG. 33 shows an embodiment where a separate energy storage element 1604is not used. In this configuration it is not possible to have the switch3108 before the Mains Rectification as there is no secondary powersource. Instead, the Mains Rectification 218 operates throughout. TheSense Circuit 206 is powered off the output of the Mains Rectificationunit 218. The switch 3108 is then placed between the Mains Rectification218 unit and all the other units (or as many as practically possible).There will be losses associated with the mains rectification. The switch3108 may also be placed at other points in the system to selectivelykeep different parts of the system running during standby.

FIG. 34 shows an embodiment where the power input is direct current. Oneapplication for this embodiment is in automotive applications. Theoperation is very similar to the FIG. 33 embodiment.

FIG. 35 shows an embodiment where a separate Sense Circuit 206 is notused. Instead the devices are detected by periodically applying power tothe primary coil 212 using a method similar to that disclosed inGB2414121 (incorporated by reference). However, this embodiment differsfrom GB2414121 in that there is an Energy Storage unit 204 present and aswitch 3502 to switch off the supply of electricity from the mains.During standby, the control unit 208 is powered from the Energy Storageelement 1604. The control unit 208 is also able to deliver power to theprimary coil 212 via the Inverter 210 from the Energy Storage element1604. Every so often power is applied to the primary coil 212 for ashort time to see if the device communicates back to acknowledge itspresence. However, the level of power required for the device tocommunicate is less than the power required to transfer full power tothe device. The control unit 208 is therefore able to activate theinverter 210 to deliver a lower level of power and therefore the amountof energy taken from the Energy Storage element 1604 is less. If thecontrol unit 208 receives a signal that a device is present, then it canswitch on the Mains Rectification 218 so that the system is powered fromthe Mains rather than the Energy Storage unit 204. If there is a validdevice present, then it can also communicate its power requirement. Thewireless power supply 200 measures the power being drawn from theprimary coil 212 and compares it to the power requirement of the device.If there is no significant difference between the two then the wirelesspower supply 200 determines that there is a valid device and no foreignobjects and therefore enables full power delivery to the device.

Instead of receiving a communication from the device that it is present,the wireless power supply 200 may simply detect that something ispresent merely by monitoring the power drawn from the primary coil 212.If the power drawn changes between successive measurements (or it isgreater than a threshold value), then either there is a device drawingthe power or alternatively a foreign object. In the current embodiment,the wireless power supply 200 determines whether there is a foreignobject present before applying full power. This method is similar to theSense Circuit 206, except that the inverter 210 is being used as theOscillator 402. In order to reduce the power consumption, to thefrequency may be shift so that it is away from resonance and there is alarge reactance to reduce power dissipation. The rail voltage applied tothe Inverter 210 may be reduced.

FIG. 36 shows an embodiment in which there are a number of primary coils212, 3606, 3608, 3610 and capacitors 214, 3616, 3618, 3620 present.These individual primary coils may each be used to supply power to aportable device. This allows multiple devices to be poweredsimultaneously. Alternatively the primary coils 212, 3606, 3608, 3610may differ from one another, so that different types of device may bepowered, for example as provided in WO2004038888. Alternatively someconfigurations of wireless power supply 200 have an array of coils, toallow a device to be positioned anywhere over a continuous area andstill receive power. An example of such a system is described inWO03105308. In a wireless power supply 200 with multiple coils, theSense Circuit 3602 may be shared across some or all the coils, savingthe need for multiple Sense Circuits 206. Every time a device (or otherobject) is placed onto the wireless power supply 200 or removed from thewireless power supply 200, the sense circuit 3602 is triggered. Theimpedance element 3622, discussed in connection with FIG. 24, isillustrated outside the sense circuit 3602 in this embodiment. Thewireless power supply unit 200 would then poll each inactive coil to seewhich coils had a valid device in proximity by closing SW2 3614 allowingthe circuits in the wireless power supply 200 to receive power, asdiscussed above. The wireless power supply 200 would then apply power tothe coils requiring power after first checking for the presence offoreign objects. In one embodiment, some devices on the power supply mayor may not desire power, for example some of the devices may have a fullbattery. Accordingly the wireless power supply may be portioned so thatsome portions are powered up and others are not.

In FIG. 36 a multipole switch 3612 is used to connect all the coils inthe wireless power supply 200 in parallel. The Sense Circuit 3602 willtrigger when a device (or object) is placed in proximity to any of thecoils 212, 3606, 3608, 3610, because any individual inductance changewill alter the overall inductance of the parallel combination. In thecurrent embodiment, the main control circuit polls each coil todetermine which should be powered. As an alternative, rather than gangall the switches together in FIG. 21, the switches may be individuallycontrolled by the MPU. In such a system, the MPU has to perform separatemeasurement for each coil. Although this means that the overalldetection time is longer (and hence standby power greater) it does meanthat the sensitivity to inductance changes will be greater.

Rather than couple the primary coils Lp1, Lp2 212, 3606, 3608, 3610, etcwith DC connections, they could be coupled by winding a few turns of asense coil around each primary coil 212, 3606, 3608, 3610. It may bepossible to eliminate some or all of the switches 3612 using thismethod.

FIG. 37 shows one embodiment of a system for minimising the power tomultiple channels for power conservation. This configuration allows anycombination of active primaries to charge or power as needed. It alsoallows the sense and sense control unit 3702 to time out each channel orprimary separately using switches 3714, 3716, 3718, and 3720 allowingeach to have independent ultra low power modes. A multipole switch 3704similar to the one used in the FIG. 36 embodiment may also be employed.Once all are powered down it can even then turn off the main power andalso control auxiliary devices and power.

In FIG. 37 each primary coil 212, 3606, 3608, 3610 has a separatedriver/control unit 3712, 3710, 3708 associated with it. Of course, asingle drive/control unit 3604 may be implemented instead as shown inthe FIG. 36 embodiment.

FIG. 38 shows one embodiment of the use of an ultra low power system ina multichannel system. Each channel or primary controller can shut downsecondary systems first and then primary for even lower powerconsumption. This system allows a DC power supply 3102 to be controlledremotely via a logic communications link.

FIG. 39 shows one embodiment of a power supply with direct power shutoff using SW2 3108 controlled by the Sense Circuit 3702.

In the embodiment illustrated in FIG. 40 a Sense Circuit that acts as aProximity Detector 4002 is used to initially detect that a device orforeign object has been placed in the vicinity of the wireless powersupply 200. It also detects if a device or foreign object is removedfrom the wireless power supply 200. This Proximity Detector 4002 iscompletely separate from the primary coil 212 and therefore notconnected to it. In one embodiment, the Proximity Detector 4002 onlyknows that a change in the devices or objects present has occurred.

Optionally, an inductive proximity sensor could be formed using anothercoil in the wireless power supply 200 which is independent of the coilused to transfer power. Another type of proximity detector 4002 thatcould be used is a capacitive proximity detector. The presence of theobject causes a change in the dielectric constant between two metalelectrodes. Alternatively the capacitance may change because of a changein mutual capacitance between the sensor and an object. Another type ofproximity detector 4002 is a Hall Effect sensor, in which there is achange in voltage in response to a change in magnetic field. Thepresence of a ferrite core or other material with similar propertieswithin the portable device may result in altering the magnetic field.

There are a number of different ways of implementing the proximitydetector 4002. An optical detector could be used, for example aphotocell device. When a device is placed on the wireless power supply200, less ambient light enters the photocell, thereby indicating thepresence of the device. False triggers generated by fluctuating lightconditions would not have a dramatic impact. Alternatively an LED orLaser could be used to generate light at visible or invisiblefrequencies and the reflected light could be detected. Another optionwould be an ultrasonic proximity detector. It is also possible to use acontact-based detector, such as a pressure switch. When a device isplaced on the wireless power supply 200, the pressure applied issufficient to make an electrical contact thus providing the same signalthat the sense circuit would provide. It is possible to have an elementin the portable device which facilitates its detection. For instance thedevice may contain a permanent magnet. When this magnet is in proximityto the wireless power supply 200 it activates a switch within thewireless power supply 200 by magnetic attraction. Additional sensecircuits that act as proximity detectors could include a hall sensor, areed switch, a motion sensor, a switch, a pressure sensor, a lightsensor, or any other sensor capable of detecting presence of an objectwithin proximity of the primary unit.

There are a number of possible configurations of Sense Circuit 206 thatcould be used. Instead of using an inductance bridge, other reactiveand/or resistive elements could be use to form the bridge. The reactiveelements may be capacitive or inductive. A resonance may be formed inorder to increase the sensitivity of the bridge to inductance changes.

In some embodiments, the separate energy source is an external means.These external means could include energy harvesting (whereby stray RFenergy in the atmosphere from RF emitting devices is extracted), solar,thermal, wind, motion energy, hydroelectric etc. Instead of using arechargeable energy source a non-rechargeable source could be used suchas a primary cell. Other forms of energy storage which could be usedinclude fuel cells. Another form of energy storage is to use the energystored in a spring. Similar techniques have been used for windup radios,lights and torches. The user could wind a handle to store energy in thespring. In another embodiment, a Mains DC power supply may provide anadditional output of a low amount of power, such as 30 mW, having itsown standby mode.

Another way of implementing the Sense Circuit 206 is for it toperiodically send out short pings of energy (for example at RF or otherfrequencies) and wait for a valid device to reply by sending a messageback on the same or a different frequency. Such pings of informationcould be transmitted using the same inductive coil or alternatively aseparate antenna may be used. Alternatively the device itself couldinitiate the process. The Sense circuit 206 could periodically listenfor pings of information so that it can determine that a device ispresent. The information could be a sinusoidal tone, or other type oftone (e.g. square or triangular wave) or a pulse sequence or aninformation packet.

The Mains Rectifier 218 may include a transformer to step down the ACvoltage, a diode bridge to convert the AC voltage to a DC voltage and asmoothing capacitor. There may also be other components such asinductors or filters to reduce ripple or for electromagnetic compliance.There may also be a DC to DC converter (which may be a switched mode DCto DC converter) to convert the DC voltage to a different DC voltage.Instead of a full diode bridge (consisting of 4 diodes) a half bridgemay used (2 diodes) or alternatively a centre-tapped transformer inconjunction with two diodes. The diodes may be Schottky diodes. Insteadof diodes, transistors (which may be MOSFET transistors) may be used toreduce the voltage drop. Techniques may be used to avoid transientsurges when the mains switch is operated. These may employ filters.Alternatively the load may be switched on gradually using a MOSFET withvariable on-resistance. Series connected switches may also be used.

In the embodiments described both the magnetic field and the inductivecoils could take a variety of forms. The field generated may beperpendicular or parallel or any other orientation with respect to thepower transfer surface. The coils could be flat spiral wound coils, withor without a magnetic core; they could be PCB coils. The coils could bewound around a ferrite rod or rectangular rod. The coils may or may nothave shielding. The coil axes may be parallel or perpendicular to thepower transfer surface. The current and/or voltage during the standbysensing would typically be much lower than during power transfer. Thefrequency applied during the sensing standby may be different to or thesame as the frequency applied during power transfer. Some or all of thevoltage, current and frequency may vary or be static during operationand/or standby sensing.

The switches could be electromagnetic relays, MOSFET transistors, solidstate relays, or other components. Latching relays are optional, they donot rely on a control voltage to be present continually and thereforethe leakage current and hence power loss will be less. However latchingrelays can be considerably more costly than non latching ones. As analternative it is possible to use non latching relays, configured sothat SW1 is open and SW4 is closed in the absence of a control voltage.An electronic latch can then be made such that when the main ControlLogic powers up, it supplies its own power to the relays to keep them inposition.

Although the operation of this invention has been illustrated in thecontext of an inductive wireless power system 200, it may alsoapplicable to other types of wireless power systems. For instance itwould be used where the energy is transmitted via RF radiation(including but not limited to microwave frequencies). The wireless powermay also be transmitted by evanescent wave coupling (e.g. Witricity).The power may also be transferred by capacitive coupling. The power mayalso be transmitted optically. Other forms of inductive, capacitive,magnetic, electrostatic or electromagnetic power transfer may be used.There is no need for the portable device to have an energy storagedevice. It is unnecessary for the wireless power transmitter to have aconnection to mains electricity. The transmitter may be powered by aninternal or external power source such as a battery, supercapacitor,fuel cell or fuel powered generator or other. Alternatively it mayderive its power by other means (e.g. energy harvesting, solar, wind,motion, thermal, hydroelectric etc.)

FIG. 41 shows the addition of controlling an auxiliary circuit using oneembodiment of the method. This could be additional equipment that wouldbe affected by this control. When SW1 202 is closed to allow mainselectricity through to the Wireless Power Supply 200, it also allows themains electricity through to the auxiliary output socket. Any equipmentconnected to this socket will also be switched on.

FIG. 42 shows one embodiment of a remote controlled auxiliary unit. Themain circuit 704 controls a signal that is sent to a second device 4202that controls additional power, for example via a switch 4204, and orfunctions as needed. The signal may be transmitted by conventional wiredconnection, optical fibre, wireless, free space optical, ultrasound etc.It should also be noted that this wireless control can be any type ofreceiver/transmitter pair or transceiver pair 4206, 4210. Some examplesof communication formats include Zigbee, ZWave, (mesh networks) currentline carrier, X10, or others. These control technologies makecontrolling other system functions 4208 easier as they are designed tocontrol appliances, thermostats, lighting and other powered devices.This can be a simple command set with commands being sent to controlexternal devices. The auxiliary unit may include a battery or otherpower source to provide some power while the mains power supply isdisconnected from a some or all of the auxiliary unit. In oneembodiment, mains power is used as the other power source to supplypower to the receive circuit while other circuitry within the auxiliaryunit is decoupled from the mains power supply.

FIG. 43 shows an alternative embodiment, similar to the FIG. 27embodiment, except that the Sense Circuit 206 transmits the signaldirectly.

FIGS. 44 and 45 show alternative embodiments whereby the wireless powersupply is integrated with another piece of electronic equipment 4402.The control circuit 208 within the wireless power system is able tocontrol the supply of power to the rest of the electronics circuitry4404, 4408.

Although the system has been illustrated in the context of a wirelesspower system, it is also applicable to other systems, where the systemcomes out of standby in response to an object, person or animal comingin proximity to it.

One possible class of system is radio frequency identification (RFID)and associated technologies such as Near Field Communications (NFC) andcontactless smart cards. In these systems information is exchangedbetween a reader 4606, 4608 and a tag 4604 or device by a radiofrequency or inductive means. The tag/device 4604 may be passive, inwhich it takes its power from the received electromagnetic power,avoiding the need for an internal battery. Alternatively the tag/device4604 may be active and have internal batteries for power. The devicestypically have an antenna consisting of a coil, transmit/receivecircuitry and a microprocessor or other logic for control. A simple tagmay be passive and simply transmit back a serial number to give itsidentity. More complex NFC devices being embedded into mobile phones cantransmit and receive information between the reader and the phone. Thereaders are used for a variety of purposes, for example cashless paymentsystems, advertising, local information. It is undesirable to for suchsystems to be permanently on, as they may not be visited frequently.

FIG. 46 shows an example of the invention being used in an RFID system(applicable to NFC and other contactless payment systems). When the RFIDtag 4604 is placed in proximity to the reader 4602, the Sense Circuit206 determines that there is tag/device in proximity. The systemtherefore connects the mains supply and powers up the reader 4602. Thereader then looks for tags/devices 4604 in proximity and communicateswith them. It is unnecessary for the reader 4602 to transfer power tothe tag/device. After the reader 4602 has finished communicating withall the tags/devices 4604 in proximity, it can re-enter the standbystate. The system remains in this state until the next change occurs(either tags/devices are removed or placed).

The above description is that of the current embodiment of theinvention. Various alterations and changes can be made without departingfrom the spirit and broader aspects of the invention as defined in theappended claims, which are to be interpreted in accordance with theprinciples of patent law including the doctrine of equivalents. Anyreference to claim elements in the singular, for example, using thearticles “a,” “an,” “the” or “said,” is not to be construed as limitingthe element to the singular.

1. A power system capable of transferring power to a portable deviceseparable from the power system, the power system comprising: a powersupply for electrical connection to a mains voltage and adapted toconvert the mains voltage into a DC voltage; and a wireless power unitelectrically coupled to the power supply DC voltage, the wireless powerunit being operable in a low-power detection mode to detect an object inproximity to the wireless power unit, the wireless power unit beingfurther operable in a power supply mode to provide wireless power to anobject in proximity to the wireless power unit, wherein the power supplyis adapted to interrupt the conversion of the mains voltage into the DCvoltage during operation of the wireless power unit in the low-powerdetection mode, the power supply being further adapted to resume theconversion of the mains voltage into the DC voltage during operation ofthe wireless power unit in the power supply mode.
 2. The power system ofclaim 1 wherein the power supply includes: a mains input for electricalconnection to a mains supply; a rectifier coupled to the mains input toconvert the mains voltage to the DC voltage; and a switch to selectivelyisolate the rectifier from the mains input during operation of thewireless power unit in the low-power detection mode.
 3. The power systemof claim 1 wherein the wireless power unit includes: a switching circuitfor converting the power supply DC voltage into an AC voltage; a sensecircuit to detect an object in proximity to the wireless power unit; anda primary coil to provide power to an object in the power supply mode.4. The power system of claim 3 wherein the power supply includes anelectrical energy storage device for providing power to the sensecircuit of the wireless power unit.
 5. The power system of claim 1wherein the wireless power unit consumes less power during the detectionmode than during the power supply mode.
 6. The power system of claim 1wherein the power supply includes a DC output and a control input, theDC output and the control input being electrically coupled to thewireless power unit through at least one cable.
 7. A power supply forelectrical connection to a device, the power supply comprising: a mainsinput for electrical connection to a mains supply; a rectifier coupledto the mains input to convert the mains supply to a DC voltage; a DCoutput to provide the DC voltage to the device; and a switch disposedbetween the mains input and the rectifier to selectively interrupt thesupply of power from the mains input to the rectifier.
 8. The powersupply of claim 7 further including a control input from the device tothe switch.
 9. The power supply of claim 7 further including anelectrical energy storage device to provide a secondary power source tothe device.
 10. The power supply of claim 7 further including a cable toelectrically connect the DC output to the device.
 11. A power supplysystem comprising: a device including a DC input; and a power supplyincluding a rectifier to convert mains power into DC power for the DCinput, the power supply including a switch to selectively allow thesupply of mains power to the rectifier in response to a control inputfrom the device.
 12. The power supply system of claim 11 wherein thedevice is operable to provide the control input in response to astimulus.
 13. The power supply system of claim 12 wherein the stimulusis provided from at least one of a receiver, a sensor, or a timer. 14.The power supply system of claim 11 wherein the device includes anenergy storage unit to provide a secondary source of power when thedevice is in a standby state.
 15. The power supply system of claim 11wherein the power supply includes an energy storage unit to provide asecondary source of power when the device is in a standby state.
 16. Thepower supply system of claim 11 wherein the device is a wireless powerunit including: a switching circuit for converting DC power into ACpower; a sense circuit to detect an object in proximity to the wirelesspower unit; and a primary coil to provide wireless power to the objectin response to detection of the object in proximity to the wirelesspower unit.
 17. The power system of claim 16 wherein the wireless powerunit is programmed to operate the primary coil in a detection mode and apower supply mode, wherein the wireless power unit consumes less powerduring the detection mode than during the power supply mode.
 18. Thepower supply system of claim 17 wherein an electrical energy storagedevice provides electrical power to the wireless power unit during thedetection mode.
 19. The power supply system of claim 16 wherein thewireless power unit is further programmed to operate the primary coil inan identification mode.
 20. The power supply system of claim 16 whereinthe sense circuit includes at least one of a hall sensor, a reed switch,a motion sensor, a switch, a pressure sensor, and a light sensor.